The present invention relates generally to improvemenets in camera electrical devices and it relates more particularly to an improved power supply switch device for a camera having an electric circuit that should be energized prior to the commencement of an exposure, such as in the case of a still camera having a light measuring circuit, an exposure control circuit or the like, or in the case of a movie camera having a sound recording circuit or a capstan driving circuit.
It is a well known practice to provide on a camera a power supply switch of the subject type which is opened and closed in conjunction with the reciprocating movement of the shutter release button for the purpose of preventing the switch from being left on or off.
The conventional mechanism, however, has certain defects in that an exposure or a sound recording may be improperly effected when the shutter release member is operated abruptly to actuate the shutter mechanism before the operation of the electric circuit thereof is sufficiently stabilized.
U.S. patent application Ser. No. 818,634, filed July 25, 1977 and assigned to the same assignee, discloses a power switch device which is turned on in response to the conductivity of the skin of the finger at the moment of the photographer touching the release button with his finger in order to overcome the above defects. The power switch device disclosed in the above application is the so-called "finger-touch responsive switch".
The power switch device disclosed in the aforesaid application has two input terminals, both related to the shutter release button, in one form the switch input terminals being connected to mutually insulated coaxial members forming part of the release button and exposed at their top and in another form such terminals being connected respectively to the camera body and an electrically insulated top exposed portion of the release button. Thus, when the release button is touched by a photographer, the switch for controlling the power supply to the camera electric circuit is electrically closed in response to the conductivity of the skin of the photographer's finger, whereby the electric circuit is supplied with electric power and energized or activated.
However, the above finger-touch responsive switch device possesses the defect that it will not operate if the photographer wears gloves. Further, with the structure disclosed in the above application, the switch may be continuously maintained in its "on" state in the event that moisture such as the sweat of the photographer or some rain drops fills the area between the two contact portions to the input terminals. This results in the waste of electric power in spite of the photographer's desire.
Furthermore, with the switch device of the above application, both contact portions which are respectively connected to the input terminals may be corroded by moisture such as sweat or the like because they are exposed externally of the camera body. As a result, the switch cannot be turned on even if the photographer touches the shutter release button with his finger.